The incorporation of additives to improve the properties and/or longevity of polymeric materials has long been recognized. Additives which may be typically employed include antifog agents, antistatic agents, antioxidants, plasticizers, UV stabilizers, non-ionic surfactants and the like.
Although certain of such additives may be added during the polymerization process, this approach may prove unsatisfactory for the incorporation of other additives. For example, the efficiency of the polymerization process may be adversely affected by interaction of the additive(s) with the polymerization catalyst, the polymer additive in question may exhibit incompatibility with other additives used in the polymerization process and/or the subsequent treatment of the polymer may be restricted by the presence of the incorporated additive at such an early stage.
Accordingly, for many additives it is necessary to employ a pre-blend of the additive and a thermoplastic polymer which contains a high level of the additive and which can, therefore, serve as a masterbatch or concentrate. The use of a master batch or concentrate is a generally preferred technique, particularly with liquid or pasty additives, as the neat use of additives having such physical form frequently gives rise to dosing problems and often requires special metering pumps or other expensive equipment.
In general, however, it has been found difficult to obtain polymer additive concentrates having an additive concentration in excess of about 10 or 15 percent by weight in the masterbatch, the maximum achievable loading depending upon the nature of the additives incorporated, their slipping properties and (due to differences in the absorption) upon the kind of polymer to be treated.
In order to overcome this problem, European Patent Application 259,960 discloses a means of greatly increasing the percentage of polymer additive in such concentrates by employing a particulate solid, preferably silica, as an absorbant for liquid, paste or waxy low-melting additives. This loaded absorbant is blended with a suitable polymer under conditions such that a super concentrate containing from 15-80 percent by weight of such an additive is formed.
However while the polymer additive concentrates of EP 259,960 will provide masterbatches having greatly increased loads of liquid, paste or waxy additives, certain drawbacks exist with respect to such concentrates. Specifically, when such concentrates are downloaded into polymers which are extruded into clear films, the silica (or other particulate filler) adversely affects the clarity of the final film.
Moreover, while the silica-containing concentrates of such publication will work admirably in opaque extrusions, it would nevertheless be desirable to possess polymer additive concentrates useful in opaque or clear polymers, which concentrates contain increased amounts of additive.
Accordingly, it is an object of this invention to provide a polymer additive concentrate which, when downloaded into polymers which are extruded into clear films, yields films having improved transparency.
It is a further object of this invention to provide a polymer additive concentrate which contains increased amounts of additive.
These objects, along with additional objects, will become more fully apparent from the following description and accompanying Examples.